Marathoners Who Slow More Have Greater Muscle Damage

Insight into why bad marathons can feel harder than good ones.

It’s common to feel much more beat up after a bad marathon than after a good one. A new Spanish study helps to explain why: Among a group of marathoners, those who slowed the most compared to their early-race pace had more post-race markers of muscle damage than runners who didn’t slow as significantly.

Researchers tracked 40 finishers of the 2012 Madrid Marathon, noting not just their 5-K splits but also physiological measures such as degree of dehydration and core temperature. After the race, the researchers gathered blood to analyze it for markers of muscle damage. The researchers divided the finishers into two groups: those who slowed less than 15% from their start pace (22 of the 40), and those who slowed more than 15% from their start pace (18 of the 40).

Race day was hot, with temperatures ranging between 70 and 90 degrees. One interesting finding was that both groups lost about the same percentage of weight. Greater dehydration, it seems, didn’t explain why one group slowed so much more than the other. Similarly, the core temperature of the runners in both groups increased by roughly the same.

There were large differences, however, between the two groups in blood markers of muscle damage. Those who slowed more than 15% from their early pace had much higher values for the three markers that the researchers measured.

In a sadistic touch, the researchers had the marathoners jump as high as possible after the marathon, and compared that to how high they could jump before the marathon. Both groups were significantly less adept at vertical jumping after the marathon, but those who had slowed the most also declined the most in this measure of leg power—their vertical jump was an average of 30% less than before the race, compared to a 23% reduction in the marathoners who had better held their pace.

The study didn’t address why some of the marathoners slowed more than others. A likely explanation is that they made the common mistake of going out too fast. That would lead to depleting their glycogen stores earlier and potentially hitting the Wall so hard that their form was affected. Running with compromised form, in turn, could easily lead to greater muscular damage.